In the prior art, automatic feeding methods that supply feed to farmed fish in preset quantities and at preset times are well-known. While such methods do allow savings to be made the labor associated with feeding work, risk of underfeeding and overfeeding is high due to the difficulty of responding to changes in the appetite of the fish. Overfeeding not only reduces profitability, but is also a cause of pollution of the sea at the site of the farm. On the other hand, underfeeding slows the growth of the fish. Also well-known as methods that aim to supply a required and sufficient quantity of feed by supplying feed in response to self-activated demand from the fish are self-activated-type feeding methods (such Japanese laid-open patent application JPA 2001-155571). However, in the self-activated type feeding systems, the self-activation behavior of the fish ceases before they are full, and these methods therefore carry the risk that the fish will not grow sufficiently (see “Youshoku” (Fish Farming) February 2009 issue, pp 5 to 8). Also, when self-activated feeding demand method is used on groups of fish, it has been reported that only a specific limited number of the individual fish behave in a way that demands feeding (Physiology and Behavior 2002, Issue 76, pp 281 to 287), and there is therefore a risk that variations in the amount of feeding will occur within the group, resulting in a loss of feeding efficiency.